.help-center-detail .box {
  background: linear-gradient(to bottom, #C8DFFF, #F4F9FF, #F4F9FF, #fff, #fff);
}
.help-center-detail .box .active-li {
  position: relative;
}
.help-center-detail .box .active-li::after {
  content: '';
  position: absolute;
  bottom: -14px;
  left: 50%;
  transform: translateX(-50%);
  width: 0%;
  height: 2px;
  background-color: #000;
  animation: open_menu 0.3s ease-in-out forwards;
}
@keyframes open_menu {
  0% {
    opacity: 0;
    width: 0%;
  }
  100% {
    opacity: 1;
    width: 40%;
  }
}